Process of spray-drying cellulose acetate solutions



Patented June 10, 1930 UNITED s'rA-raa A ENT.- OFFICE GYBIL J. STA'UD, OI ROCHESTER, NEW YORK; ASSIGNOB .lO mm: KODAK comm,

OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK ,Ho DrawingJ This invention relates to spray-drying of cellulose acetate solutions,-especially t ose containing acetic acid. One object of the invention is to provide a spray-drying process I for converting such solutionsinto a powder of with the cellulose acetate and acetic acid, an

organic liquid of hi h volatility relative to water, for exampleg, such as et ylene dichlorid, such solution being spray-dried, as described in-U. S. Patent No. 1,516,225, Webb, Nobember.18,1924. The presence of this volatile liquid causes the particles'to present a jagged broken outer surface, the violent evolution of the volatile liquid during the drying operation causing a condition in the particles 2 roughly analogous to the pulling action of the steam in puffed cereals. In other words, not only are the particles individually verysmall, relative to those usually obtained by spraydrving' acetate reaction mixtures, but these individual particles are particularlg permeable to'treating liquids, such as hy rolyzing baths and washing baths.

I shall'now describe one-way .of carnying out my invention, for purposes of illustration,

but it will be understood that the invention is not limited to the details thus given, except as indicated in the "appended claims. 100 parts by weight of cellulosic material, say purified and bleached cotton fibers, for example, are immersedfor three and one-half hours at av tem erature between 20 C. and 40 0., u say 35 with 600 parts by wei ht of glacial acetic acid mixed with .18 artsdw weight of sulfuric acid and 5.4 parts y weight of ortho phosphoric acid. At the end of the above mentioned time, the excess of li uid is. removed by pressure so that the weig t of acetic acid in the press-cake is substantially equal to the wei ht of the cellulosic material. The

59 press-ca e is then thoroughly mixed up with Application filed larch 2, i928. Serial in. 258,689. 7 l.

income orsrnavrnnnne CELLULOSE acn'ra'rn summons 2 248 parts by weight of actual acetic anhydrid V and 400 to 600 parts by weight of ethylene dichlorid. If the mixture heats too much, it should be restrained, and the mixing can, therefore, be most conveniently done in a re-' actlon vessel provided with cooled walls. Good results are obtained'by keeping the reaction mass between 33 C. and C. with agitation until a clear flowable dope is obtamed. Then there is thoroughly mixed in on the dope about 400 parts by weight more of ethylene dichlorid. that thedesired objects can This dope, after be filtered ifnccesary is' then spray-dried accordaiice with th: process described in detail in the above cited 66 Webb patent. The above described reaction dope 1s blown, under considerable pressure, through 'a nozzle into a fine spray or mist whlchfcomes ingloy intimate contact with a current 0 warm, air, actin as-a desicca vehicle. The acetic acid End ethylene d i chlorid evaporate very rapidly from the par- 1 ticles of the mist, leaving the atter as a powder, havingthe puffed characteristics hereinabove described. V (I In the above example, of addin 400 parts of ethylene dichlorid at the close 0 the reaction, I may-add 1000 parts by wei ht of this origmally. My process is applica 1e :to' the spray-drying of cellulose acetate reso action do ea or mixtures at the several sta 2- of manu 'acturej In the above exam le, or instance, my process is carried out when the cellulose acetate has reached the chloroformsoluble stage; It may, however, he carried out when the reaction mixture is in the form of'a flowable dope containing acetone-soluble cellulose acetate dissolved in a mixture containing acetic acid. Insuch a case, I add a volume of ethylene diehlorid to the dope,

equal to the volume of the latter,in other words, doublin the volume of the dope by the addition 0 ethylene dichlorid. I may likewise obtain chloroform-soluble cellulose acetate by an of the known methods which produce a so ution in acetic acid, and then dilute said dope with an equal volume of ethylene dichlorid. When all of these mixtures cont the volatile organic H 'd are spray-dried,',tlie finely divided %d broken-surfaced particles are obtained. The more ethylene dichlorid used, the finer the rough-surfaced particles. For example, in-

' stead of adding an equal volume of theethylene dichlorid to a reaction dope before sprai- 'ing, I may add twice as much ethylene ch orid as the volume of dope, thus making the final mixture for spra -dryingequal to three times the volume of t e ori al.

Ethylene. dichloridcan be replaced y Organic quids miscible with acetic acid and cellulose acetate in the dopes such as ethylene trichlorid .and even chloroform.

But I prefer to use ethylene dichlorid, be-

cause it is so readily separable from the acetic acid with which it is recovered in the spra drying process. It can be'fractionally distilled away, and in doing so, will dehydrate the acetic acid. 1 o I Having thus described my invention, what ll claim as new and desire to secure by Letters Patent is:

1. In the process of prepar'cellulose acetate, spraying in e droplets a. fiowahle reaction mixture comprising cellulose acetate, acetic acid and an organic liquid which is miscible therewith and highly volatile,

into a desiccating gaseous vehicle which takes up vapors of acetic acidand of said liquid with great rapidity therehy disrupting the partic es and converting the spray into a fine power the particles of which are rough sur faced and highly permeable-to liquids.

2. In the acetate, atomizing a fiowahle solution of cel-' lulose acetate in aceticacid andethylene di-' chlcrid into a desiccating gaseous vehicle which takes up va ore of acetic acid and ethylene dichlorid with great ra idity, thereby disrupting the particles an converting them into a fine powder the articles of which are rough surfaced and hig y permeable to liquids. v

3. In the process of preparing cellulose acetate, atomizmg flowable solution of cellulose acetate in acetic acid and ethylene dichlorid into a desiccating gaseous vehicle which takes up vapors of acetic acid and ethylene dichlorid with great rapidity, thereby disrupting the particles and converting them into a fine powder the particles of which are -rou h surfaced and highly rmeable to liqui s,

separating said vaporaden gaseous vehicle from said powder and recovering said acid and said dichlorid from said vehicle.

Signed at Rochester, New York, this 27th day of Feb. 1928.

CYRE .l'. STAUD.

process of preparing cellulose 

